Nonlinear optical materials have been disclosed, for example, in Journal of Optical Society of America, Vol. 73 (1983), p. 647. These materials comprise a cut-off filter glass formed of borosilicate glass with a semiconductor CdS.sub.x Se.sub.1-x wherein X is 0 to 1 dispersed therein. The material is produced by melting a mixture of CdS.sub.x Se.sub.1-x and borosilicate glass, quenching the mixture to disperse ions of Cd, S and Se in the borosilicate glass, reheating it to 600.degree. to 700.degree. C., and precipitating fine particles of CdS.sub.x Se.sub.1-x throughout the glass. The mean particle diameter of the particles is dependent on temperature and time of reheating; The mean particle diameter is proportional to the reheating time to the one-third power.
Another thin film glass dispersed with CdS fine particles is disclosed in Journal of Applied Physics, Vol. 63 (1988), p. 957. This glass is produced by the high frequency magnetron sputtering method using CdS and a Ba-containing borosilicate glass by dispersing 2 to 4 at .% of CdS throughout the borosilicate glass and reheating the glass to 400.degree. to 500.degree. C. for about 24 h to precipitate fine CdS particles. The mean particle diameter of the CdS particles is also proportional to the reheating time to the one-third power.
The smaller and more homogeneous the particle size distribution of a semiconductor fine particle dispersed in a glass matrix, the more optical effects are provided. An appropriate content or composition of the semiconductor is desired.
Conventional methods of producing nonlinear optical materials from glass having semiconductor fine particles dispersed therein had the following problems; Melting a mixture of CdS.sub.x Se.sub.1-x and borosilicate glass at high temperatures and reheating it enlarges the particle size distribution of the dispersed semiconductor fine particles too much. When the content of the semiconductor in the material is above 4 at .%, its particle diameter becomes too large to be a fine particle. Such an inappropriately large particle size affects nonlinear optical properties. In other words, large particles make the glass white or clouded or reduce the intensity of the emission spectrum of the semiconductor in the vicinity of optical adsorption.
With the high frequency magnetron sputtering method, a long heat treatment time enlarges the particle size distribution of the semiconductor fine particles too much.
With the sputtering method, the composition change of the semiconductor in the thin film occurs due to the evaporation of the semiconductor; Of the compositions of the semiconductor material, some elements easily evaporate or sublime so that the composition of the semiconductor deviates from the original composition. The particle diameter of the semiconductor similarly increases with the content of the semiconductor.